Two sets of strikes 30 minutes apart hit civilians sheltering in tents along the Euphrates and boats on the river, the monitor said.

They come as the Syrian army prepares to push into the eastern IS-held part of Deir Ezzor city, according to the Observatory.

"Huge military reinforcements, including equipment, vehicles and fighters have arrived in Deir Ezzor ahead of an attack to push Daesh from the city's eastern neighbourhoods," said Observatory chief Rami Abdel Rahman, using an Arabic acronym for IS.

"Russian and Syrian regime warplanes are striking IS positions in the city and its outskirts," he added.

Since 2014, IS has controlled most of Deir Ezzor city and the surrounding province, which borders territory the jihadists hold in Iraq.

The remaining 40 per cent of the city still held by the government -- and home to around 1,00,000 civilians -- was under crippling IS siege.

Backed by Russian air power, government troops have breached IS's sieges, captured the strategic Jabal Thardah region and expanded their control to half of Deir Ezzor city.

Moscow intervened in Syria in September 2015 in support of its ally President Bashar al-Assad.

Fighters from the US-backed Syrian Democratic Forces on Saturday announced a separate offensive to capture IS territory east of the Euphrates river, which slices diagonally across Deir Ezzor province.

By today, the SDF's Deir Ezzor Military Council (DEMC) had seized much of the province's northeast and were just a few kilometres away from the river.

Abdel Rahman said they had advanced to six kilometres from its eastern banks, at a point across the river from Deir Ezzor city.

Colonel Ryan Dillon, spokesman for the US-led coalition backing the SDF, said the militia had made "significant gains", capturing around 250 square kilometres since the operation began.

The SDF, an alliance of Arab and Kurdish fighters, is also battling IS in the jihadists' de facto capital Raqa with backing from the US-led air coalition.

Although the SDF has yet to reach Deir Ezzor city itself, tribal figures affiliated with the alliance said they were laying the groundwork for governing the city after IS's defeat.

The statement, published by the SDF's media council, announced the establishment of "a preparatory committee that will discuss the basis and starting points for a civil council for Deir Ezzor".

According to the statement, consultations would aim to reach a "formulation that will express the aspirations of all our people in Deir Ezzor".

The Deir Ezzor Civil Council "will be responsible for running the city immediately after its liberation".

It made no mention of regime forces and did not say whether the civil council would coordinate with, or rival, government authorities.

The SDF has said its assault in Deir Ezzor province is not in coordination with Russian or regime forces.

But the coalition, the SDF, Syria's government and Russia have agreed on a "de-confliction line" in northeastern Syria to prevent the two offensives from clashing.

Aaron Stein, a senior fellow at the Atlantic Council's Rafik Hariri Center for the Middle East, said he did not expect the SDF to enter Deir Ezzor city.

But, he added, "the SDF is now racing. The SDF is in a race with the regime."

"The regime forced everyone's hand. They moved faster than expected up the river, so things started to move."

Syria's conflict erupted in 2011 with protests calling for Assad's ouster, but it has since evolved into a complex war drawing in world powers.

More than 3,30,000 people have been killed and millions have been forced to flee their homes.

(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)